I served stateside in the late 90s. Certain of the areas I worked in had established ongoing service projects that we would do for four hours every week--if you were a missionary in that particular area, you did that particular service project every week. These included:
1) Helping babysit kids at an economic crisis center so the parents could have a break. We did two two-hour "supervised chaos" sessions at the shelter every week.
2) Working as teaching assistants at a local elementary school. Again, we would do two two-hour sessions at the school every week; sometimes we'd help tutor the kids or help them read, other times we'd just run errands for the teachers (making copies, laminating teaching materials, etc.).
3) Working as a volunteer at a community hospital--again, two two-hour sessions per week. We'd basically sit in a room with a phone and would respond to calls to wheel patients out of the hospital; run materials from one department to another, etc.
Near the end of my mission, a rule came down from on high about how missionaries were no longer permitted to do any service activities where the missionaries would be with children, so I'd imagine that numbers 1) and 2) above got discontinued out of concern for any missionaries behaving inappropriately with the kids, though neither of those situations involved any time where a missionary was alone with a kid where they could not be observed.
Like other posters, we were always expected to wear our proselytizing outfits while doing service, though proselytizing was not supposed to be the point of it (well, except to zealous missionaries who just couldn't fathom helping someone without expecting a conversion in return). In some areas where there were not established service projects, we'd just arrange things on our own, which generally turned out to be helping someone move, painting a house, etc. We did get reprimanded for spending more than four hours in service activities per week--but as noted above, sometimes it was just nice to fill the time with something other than tracting. That happened one time when we were painting an investigator's house--we spent lots of hours painting in the hopes that they'd take the discussions, and I think they only took one. Sad that we were so disappointed by that.
I remember that we also volunteered with a community center that would host dinners and other community functions and the missionaries would effectively serve as the wait staff. I remember some missionaries having a problem with serving people coffee as part of the function since they were "morally opposed" to drinking coffee. I also remember that particular service being funny because apparently all of the other wait staff were various delinquents who had been forced to do the service as part of their discipline, so the patrons were always surprised how polite the missionaries were since they were used to being waited on by the delinquents.